diff --git a/packet_packer.go b/packet_packer.go
index c96307cbc..9d3073d73 100644
--- a/packet_packer.go
+++ b/packet_packer.go
@@ -215,7 +215,7 @@ func (p *packetPacker) PackConnectionClose(ccf *wire.ConnectionCloseFrame) (*pac
 		hdr = p.getShortHeader(s.KeyPhase())
 	}
 
-	return p.writeAndSealPacket(hdr, payload, encLevel, sealer)
+	return p.writeSinglePacket(hdr, payload, encLevel, sealer)
 }
 
 func (p *packetPacker) MaybePackAckPacket(handshakeConfirmed bool) (*packedPacket, error) {
@@ -251,7 +251,7 @@ func (p *packetPacker) MaybePackAckPacket(handshakeConfirmed bool) (*packedPacke
 	if err != nil {
 		return nil, err
 	}
-	return p.writeAndSealPacket(hdr, payload, encLevel, sealer)
+	return p.writeSinglePacket(hdr, payload, encLevel, sealer)
 }
 
 // PackPacket packs a new packet.
@@ -357,7 +357,7 @@ func (p *packetPacker) packCryptoPacket(
 		payload.frames = []ackhandler.Frame{{Frame: cf}}
 		payload.length += cf.Length(p.version)
 	}
-	return p.writeAndSealPacket(hdr, payload, encLevel, sealer)
+	return p.writeSinglePacket(hdr, payload, encLevel, sealer)
 }
 
 func (p *packetPacker) maybePackAppDataPacket() (*packedPacket, error) {
@@ -403,7 +403,7 @@ func (p *packetPacker) maybePackAppDataPacket() (*packedPacket, error) {
 		p.numNonAckElicitingAcks = 0
 	}
 
-	return p.writeAndSealPacket(header, payload, encLevel, sealer)
+	return p.writeSinglePacket(header, payload, encLevel, sealer)
 }
 
 func (p *packetPacker) composeNextPacket(maxFrameSize protocol.ByteCount) payload {
@@ -529,15 +529,37 @@ func (p *packetPacker) getLongHeader(encLevel protocol.EncryptionLevel) *wire.Ex
 	return hdr
 }
 
-func (p *packetPacker) writeAndSealPacket(
+// writeSinglePacket packs a single packet.
+func (p *packetPacker) writeSinglePacket(
 	header *wire.ExtendedHeader,
 	payload payload,
 	encLevel protocol.EncryptionLevel,
 	sealer sealer,
 ) (*packedPacket, error) {
+	packetBuffer := getPacketBuffer()
+
+	n, err := p.appendPacket(packetBuffer.Slice[:0], header, payload, encLevel, sealer)
+	if err != nil {
+		return nil, err
+	}
+	return &packedPacket{
+		header: header,
+		raw:    packetBuffer.Slice[:n],
+		ack:    payload.ack,
+		frames: payload.frames,
+		buffer: packetBuffer,
+	}, nil
+}
+
+func (p *packetPacker) appendPacket(
+	raw []byte,
+	header *wire.ExtendedHeader,
+	payload payload,
+	encLevel protocol.EncryptionLevel,
+	sealer sealer,
+) (int, error) {
 	var paddingLen protocol.ByteCount
 	pnLen := protocol.ByteCount(header.PacketNumberLen)
-
 	if encLevel != protocol.Encryption1RTT {
 		if p.perspective == protocol.PerspectiveClient && header.Type == protocol.PacketTypeInitial {
 			headerLen := header.GetLength(p.version)
@@ -549,27 +571,17 @@ func (p *packetPacker) writeAndSealPacket(
 	} else if payload.length < 4-pnLen {
 		paddingLen = 4 - pnLen - payload.length
 	}
-	return p.writeAndSealPacketWithPadding(header, payload, paddingLen, encLevel, sealer)
-}
-
-func (p *packetPacker) writeAndSealPacketWithPadding(
-	header *wire.ExtendedHeader,
-	payload payload,
-	paddingLen protocol.ByteCount,
-	encLevel protocol.EncryptionLevel,
-	sealer sealer,
-) (*packedPacket, error) {
-	packetBuffer := getPacketBuffer()
-	buffer := bytes.NewBuffer(packetBuffer.Slice[:0])
 
+	hdrOffset := len(raw)
+	buffer := bytes.NewBuffer(raw)
 	if err := header.Write(buffer, p.version); err != nil {
-		return nil, err
+		return 0, err
 	}
 	payloadOffset := buffer.Len()
 
 	if payload.ack != nil {
 		if err := payload.ack.Write(buffer, p.version); err != nil {
-			return nil, err
+			return 0, err
 		}
 	}
 	if paddingLen > 0 {
@@ -577,40 +589,29 @@ func (p *packetPacker) writeAndSealPacketWithPadding(
 	}
 	for _, frame := range payload.frames {
 		if err := frame.Write(buffer, p.version); err != nil {
-			return nil, err
+			return 0, err
 		}
 	}
 
 	if payloadSize := protocol.ByteCount(buffer.Len()-payloadOffset) - paddingLen; payloadSize != payload.length {
-		fmt.Printf("%#v\n", payload)
-		return nil, fmt.Errorf("PacketPacker BUG: payload size inconsistent (expected %d, got %d bytes)", payload.length, payloadSize)
+		return 0, fmt.Errorf("PacketPacker BUG: payload size inconsistent (expected %d, got %d bytes)", payload.length, payloadSize)
 	}
 	if size := protocol.ByteCount(buffer.Len() + sealer.Overhead()); size > p.maxPacketSize {
-		return nil, fmt.Errorf("PacketPacker BUG: packet too large (%d bytes, allowed %d bytes)", size, p.maxPacketSize)
+		return 0, fmt.Errorf("PacketPacker BUG: packet too large (%d bytes, allowed %d bytes)", size, p.maxPacketSize)
 	}
 
-	raw := buffer.Bytes()
-	_ = sealer.Seal(raw[payloadOffset:payloadOffset], raw[payloadOffset:], header.PacketNumber, raw[:payloadOffset])
+	raw = raw[:buffer.Len()]
+	_ = sealer.Seal(raw[payloadOffset:payloadOffset], raw[payloadOffset:], header.PacketNumber, raw[hdrOffset:payloadOffset])
 	raw = raw[0 : buffer.Len()+sealer.Overhead()]
 
 	pnOffset := payloadOffset - int(header.PacketNumberLen)
-	sealer.EncryptHeader(
-		raw[pnOffset+4:pnOffset+4+16],
-		&raw[0],
-		raw[pnOffset:payloadOffset],
-	)
+	sealer.EncryptHeader(raw[pnOffset+4:pnOffset+4+16], &raw[0], raw[pnOffset:payloadOffset])
 
 	num := p.pnManager.PopPacketNumber(encLevel)
 	if num != header.PacketNumber {
-		return nil, errors.New("packetPacker BUG: Peeked and Popped packet numbers do not match")
+		return 0, errors.New("packetPacker BUG: Peeked and Popped packet numbers do not match")
 	}
-	return &packedPacket{
-		header: header,
-		raw:    raw,
-		ack:    payload.ack,
-		frames: payload.frames,
-		buffer: packetBuffer,
-	}, nil
+	return len(raw) - hdrOffset, nil
 }
 
 func (p *packetPacker) SetToken(token []byte) {